Acoording to The Guardian's readers, one one of the 10 best ruins in the UK is Maunsell Sea Forts, Thames and Mersey estuaries. These coastal defence forts were built in the Thames and Mersey estuaries during the second world war to deter German raids. After the war, several of the forts in the Thames estuary became hubs for broadcasting pirate radio, and one became the infamous micronation the Principality of Sealand. Others still are rusty relics on the verge of being claimed by the sea, and as Bernicianscots notes, “They have an eerie beauty about them.”